In manufacturing semiconductor devices such as LSI and super-LSI or in manufacturing a liquid crystal display board or the like, there is a process wherein a pattern is made by irradiating light to a semiconductor wafer or an exposure original plate for liquid crystal. On this occasion, a method is used whereby a surface of the exposure original plate is roofed by a pellicle bearing a pellicle membrane which transmits the light for exposure well, for the purpose of fending off the dust from the plate.
A typical conventional pellicle and a mask are shown in FIG. 1. In this figure, the reference numeral 1 designates the pellicle, 2 a pellicle frame, 3 a mask-bonding agglutinant, and 4 the mask (which can be a reticle).
In general a pellicle is built up of a pellicle frame, which is made of aluminum or a stainless steel or polyethylene or the like, and a transparent pellicle membrane made of cellulose nitrate or cellulose acetate or a fluorocarbon polymer or the like, which transmits light well; this membrane is attached to one of the two frame faces (hereinafter referred to as “membrane-receiving frame face” or “membrane-bearing frame face”) by means of an adhesive made of a substance such as acrylic resin, epoxy resin and a fluorocarbon polymer; furthermore, on the other one of the two frame faces (hereinafter referred to as “mask-side frame face”) is laid an agglutinant layer made of a polybutene resin, a polyvinyl acetate resin, an acrylic resin, a silicone resin or the like, and over this agglutinant layer is laid a releasable liner (separator) for protecting the agglutinant layer.
The pellicle has been designed to prevent the environmental dust from adhering to surfaces of the exposure original plate; in recent years, as the wavelengths of the exposure lights are shifted toward shorter sizes, the light energy is strengthened with shortening of the wavelengths so that the rapidity at which the agglutinant and the adhesive decompose as they are exposed to the lights is heightened so much that it became necessary to design a pellicle which has a structure such that the agglutinant and the adhesive are not exposed to the light or such that, even though the agglutinant and the adhesive are exposed to the light, the light-decomposed agglutinant or adhesive does not release a dusty particle into a space enclosed by the pellicle and the mask (ref. Publication-in-patent 1). At the same time, a demand for materials which do not easily decompose as they are exposed to such strong exposure lights exists; however, there has not been found a material that has qualities sufficiently answering the demand.
Consequently, a problem has arisen wherein, when a mask attached with a pellicle is used, a haze (incremental foreign material) is grown on the mask. The occurrence frequency of this problem has increased especially as the ArF has become the prevailing light source.
One cause for this problem is thought to be the out-gassing. In FIG. 2 is shown a situation wherein out gases 7 are released some into the space enclosed by the pellicle and the mask as shown by some of the broken arrow lines. The reference numeral 5 designates the pellicle membrane, and 6 the adhesive to bond pellicle membrane. The pellicle closed space (the space enclosed by the pellicle and the mask) is occupied by the out gases from the pellicle and other gases, and when the exposure light such as an ArF laser ray hits the out gases a photochemical reaction takes place and this may produce haze.
Among the out gases from the pellicle those from the mask-bonding agglutinant is the greatest in amount. This is because of the facts, among others, that the agglutinant is the largest in volume among the organic components of the pellicle, that the agglutinant contains low molecular weight elements or chemically unstable elements for better adhesiveness, and that the agglutinant is made of a material which is moderately easy to wash off, i.e., easy to chemically decompose with a view of easy detachment of the pellicle from the mask after use. There have been efforts to reduce the amount of the out gases from the agglutinant with a modicum of success, but so long as the agglutinant is made to have high adhesiveness, an epoch-making reduction in out-gassing is not foreseen.